Ball coupling device with hinged connection for two sliding shafts

ABSTRACT

The invention relates to a device for coupling an inner shaft and an outer shaft sliding in the direction of a common axis thereof, with balls provided between the two shafts. The balls are arranged in axial grooves of the inner shaft and in axial grooves of the outer shaft. Each row of balls is maintained by a double elastic member that bears in the groove of the inner shaft and urges the balls along two rolling tracks so that they come into contact with the groove of the outer shaft, wherein each of the two rolling tracks is hinged through a pivot surface and a bearing surface of the corresponding shaft, and the difference between the radii defines two bearing areas defining a hinge axis parallel to the common axis.

CROSS-REFERENCE TO RELATED APPLICATIONS)

This is a national phase application under 35 U.S.C. §371 of PCTApplication No. PCT/FR2008/000874, filed Jun. 20, 2008, the contents ofwhich are expressly incorporated herein by reference.

FIELD OF ART

The invention relates to a device for rotatably coupling two slidingshafts along the common axis thereof. The coupling device of theinvention particularly applies to an automotive vehicle steering column,by adapting it to the intermediate column portion connected to thesteering gear case or to the upper column portion connected to thesteering wheel.

BACKGROUND

In the more particular case of the intermediate axis, the latter has aCardan joint at each end: one Cardan joint is connected to the motioninput of the steering gear case, and the other Cardan joint is connectedto the upper column portion. In order to have correct steering ofcurrent automotive vehicles, it is required that the length of theintermediate axis be able to vary and adapt to the oscillations of thefront gear of the vehicle, due to the profile and the surface conditionof the road carpet. This characteristic is also required in order tomake the assembling to the rack pinion easier, and to absorb motionsupon a frontal impact of the vehicle.

The intermediate axis should therefore have first a variable length,that is it should have a sliding function of two shafts with respect toeach other along the column axis thereof, which is the intermediateportion axis. Moreover, a transmission function for the rotationmovement between the two shafts and for the torque necessary forhandling the steering is required.

There are numerous sliding shaft coupling devices, which enable tocombine the passing of the torque between the two shafts through splineswhich are provided on each of the two shafts with conjugated profiles.However, this type of device has a clearance after an endurance cycleequivalent to the service life of a vehicle, which is the one requiredfor current cars. In order to delay the onset of such clearance,adjusting the sliding of both shafts upon manufacture is relativelytight, which requires upon the line assembly a quite high axial stress,hence a longer assembly time and more laboriousness upon such mounting.

Such adjustment should be accurate in order to enable operational axialmovements to be correctly absorbed. Except upon the passing of thetorque, the axial stress is a function of the torque being transmitted,the sliding stress related to the torque being transmitted and thefriction coefficient increases, and then there is a sudden axialrelease, causing jerks which prevent a good sliding adjustment withreduced clearance to be maintained; and being harmful for a good drivingfeeling.

There are also coupling devices which use plastic injection on splinedportions which are part of a male metal shaft and a female metal tube.This solution raises issues for absorbing axial movements under hightorques; the sliding stresses increase proportionally to the frictionforces between the two portions. Besides, the plastic injection wearleaves clearances. As a last solution, rolling elements and strainsprings can be introduced between the shaft and the tube. Thissatisfying solution for a smooth sliding raises issues of angularrigidity because it is directly proportional to the stiffness andpreloading of the springs.

SUMMARY

The object of the present invention is to provide a coupling device forsliding shafts which avoids the previous drawbacks, that is a devicewhich requires an axial stress not related to the torque to betransmitted. The axial stress should therefore experience a very smallincrease when the torque to be transmitted increases while having astrong angular rigidity of the transmission. Further, there should notbe any clearance after the endurance cycle and the coupling device ofboth shafts should be able to be easily mounted in the possible existingovercrowdings on automotive vehicles and this with a reduced axialstress upon assembling.

More precisely, the object of the invention is:

reducing contact pressures due to the transmitted torque, in order toimprove the service life of the product and maintain the initialcharacteristics;

-   -   making the assembly easier and absorbing the size and geometry        tolerances of the different components;

not biasing the elastic member too much; and minimising the slidingstress variation and improving the characteristics of a priorapplication on the name of the Applicant NACAM.

The invention relates to a coupling device for two shafts: an innershaft and an outer shaft which slide into each other in the direction ofthe common axis thereof. Said coupling device for both shafts comprisesballs, which are provided between the inner shaft and the outer shaft.

In the coupling device, each of said balls is arranged, in the one hand,in a concave portion of the inner shaft and, on the other hand, in aconcave portion of the outer shaft.

Each of said balls moves along two rolling tracks arranged on eitherside of a median plan going through the common axis and the centre ofsaid balls. Each of the two rolling tracks cooperates with the concaveportion of one of the two shafts, which are all parallel to the commonaxis. Each of the two rolling tracks is pushed by an elastic memberbearing in said concave portion, each of said balls moving directlyagainst the concave portion of the other shaft.

Each of the two rolling tracks has a bearing portion with a bearing sideof each of said balls, and a pivot portion with a rounded pivot sideapplied against a rounded support side of the corresponding concaveportion of the shaft. According to an essential characteristic of theinvention, the radius of the support side of the shaft is different fromthe radius of the pivot side of the rolling track, in order to have twocontact areas which define the position of a joint axis of the pivotbeing parallel to the common axis.

The mounting is carried out such that at rest, when there is no torquetransmission, and in operation, when there is a torque transmission,each of said balls is always in contact on either side of the medianplan, through a bearing area with the corresponding rolling trackarranged in one of the two shafts, and through a bearing area with theconcave portion of the other shaft.

According to some embodiments of the invention, the radius of theconcave support side of the shaft is smaller than the radius of theconvex pivot side of the rolling track; and in other embodiments, theradius of the support side of the shaft is convex and larger than theradius of the concave pivot side of the rolling track. In all theseembodiments and for each of the two rolling tracks, the radii of thesupport side of the shaft and the pivot side of the rolling track can beconstant or progressive. Further, the bearing portion has a bearing sideof the balls, which can be plane, convex, concave or with doubleconcavity.

In order to increase the operating safety of the coupling device of theinvention, male grooves and female grooves, having conjugated profileswith some clearance, are arranged on the inner shaft and on the outershaft, such that in case the balls are lost, the torque can still betransmitted between the inner shaft and the outer shaft.

Several structures of the coupling device can be designed. In onestructure, the elastic member(s) is or are provided in the inner shaft.In another structure, the elastic member(s) is or are provided in theouter shaft.

In another structure, some of the elastic members are provided in theinner shaft and the others in the outer shaft.

In a particular arrangement of the invention, the coupling device hasthe balls being located in several axial rows.

For each row of balls, there is provided in the outer shaft a concaveportion having the shape of an axial groove, the section of whichcomprises two concave sides being tilted with respect to each other,which come into contact with the balls.

For each row of balls, there is provided in the inner shaft a concaveportion having the shape of an axial groove, the section of whichcomprises a bottom and two flanks, the bottom being substantiallyperpendicular to the median plan going through the common axis and theaxis of the centres of the balls in said row.

For each row of balls, two rolling tracks are arranged on either side ofthe median plan and cooperate with the concave portion having the shapeof an axial groove of the inner shaft. Each rolling track has the shapeof an axial bar, the section of which has a bearing portion and a pivotportion.

The bearing portion has a bearing side determined to come into contactwith the balls. The pivot portion has a rounded shape with a convexpivot side, which cooperates with a concave rounded support side,joining the bottom and the corresponding flank of the axial groove, inorder to have two contact areas determining the position of the jointaxis of the pivot being parallel to the common axis. Each of the tworolling tracks is pushed by a spring which bears on the bottom of theaxial groove.

In another particular arrangement of the invention, the coupling devicehas the balls being arranged in several axial rows.

For each row of balls, there is provided in the inner shaft a concaveportion having the shape of an axial groove, the section of whichcomprises two concave sides being tilted with respect to each other,which come into contact with the balls.

For each row of balls, there is provided in the outer shaft a concaveportion having the shape of an axial groove, the section of whichcomprises a bottom and two flanks, the bottom being substantiallyperpendicular to the median plan going through the common axis and theaxis of the centres of the balls in said row.

For each row of balls, two rolling tracks are arranged on either side ofthe median plan and cooperate with the concave portion having the shapeof an axial groove of the outer shaft. Each rolling track has the shapeof an axial bar, the section of which has a bearing portion and a pivotportion.

The bearing portion has a bearing side determined to come into contactwith the balls. The pivot portion has a rounded shape with a convexpivot side, which cooperates with a concave rounded support side joiningthe bottom and the corresponding flank of the axial groove, in order tohave two contact areas determining the position of the joint axis of thepivot being parallel to the common axis. Each of the two rolling tracksis pushed by a spring which bears on the bottom of the axial groove.

In another particular arrangement of the invention, the coupling devicehas the balls being arranged in several axial rows.

For each row of balls, there is provided in the outer shaft a concaveportion having the shape of an axial groove, the section of whichcomprises two concave sides being tilted with respect to each other,which come into contact with the balls.

For each row of balls, there is provided in the inner shaft a concaveportion having the shape of an axial groove, the section of whichcomprises a bottom and two flanks, the bottom being substantiallyperpendicular to the median plan going through the common axis and theaxis of the centres of the balls in said row.

For each row of balls, two rolling tracks are arranged on either side ofthe median plan and cooperate with the concave portion having the shapeof an axial groove of the inner shaft. Each rolling track has the shapeof an axial bar, the section of which has a bearing portion and a pivotportion.

The bearing portion has a bearing side determined to come into contactwith the balls. The pivot portion has a rounded shape with a concavepivot side, which cooperates with a convex rounded support side joiningthe bottom and the corresponding flank of the axial groove, in order tohave two contact areas determining the position of the joint axis of thepivot being parallel to the common axis. Each of the two rolling tracksis pushed by a spring which bears on the bottom of the axial groove.

In another particular arrangement of the invention, the coupling devicehas the balls being arranged in several axial rows.

For each row of balls, there is provided in the inner shaft a concaveportion having the shape of an axial groove, the section of whichcomprises two concave sides being tilted with respect to each other,which come into contact with the balls.

For each row of balls, there is provided in the outer shaft a concaveportion having the shape of an axial groove, the section of whichcomprises a bottom and two flanks, the bottom being substantiallyperpendicular to the median plan going through the common axis and theaxis of the centres of the balls in said row.

For each row of balls, two rolling tracks are arranged on either side ofthe median plan and cooperate with the concave portion having the shapeof an axial groove of the outer shaft. Each rolling track has the shapeof an axial bar, the section of which has a bearing portion and a pivotportion.

The bearing portion has a bearing side determined to come into contactwith the balls. The pivot portion has a rounded shape with a concavepivot side which cooperates with a convex rounded support side joiningthe bottom and the corresponding flank of the axial groove, in order tohave two contact areas determining the position of the joint axis of thepivot being parallel to the common axis.

Each of the two rolling tracks is pushed by a spring which bears on thebottom of the axial groove.

According to different embodiments of the invention, each of the tworolling tracks is pushed by an elastic member which is a spring bearingon the bottom of the axial groove.

The spring is made of a body provided with elastic members, andcomprising an axial edge on either side and a staple at each axial end;said body being mounted in the bottom of the corresponding concaveportion of the shaft and having a shape conjugated with said bottom,that is bulged or convex, having at each transverse end a concave shapereceiving the corresponding axial edge of said spring, of which bothstaples hold on the corresponding shaft. The elastic members aretransverse tabs arranged directly by cutting the body, said tabs beingheld alternatively on one axial edge, then on the other edge.

In a particularly well-balanced assembly of the coupling device, theballs are arranged in three axial rows. The axial rows are transverselylocated at 120° from one another. The inner shaft is provided with threeaxial grooves, the axial grooves being transversely located at 120° fromone another. The outer shaft is provided with three axial grooves, theaxial grooves being transversely located at 120° from one another.

In another particularly well-balanced assembly of the coupling device,the balls are arranged in two diametrically opposed axial rows. Theinner shaft is provided with two diametrically opposed axial grooves.The outer shaft is provided with two diametrically opposed axialgrooves.

In a complete architecture of the coupling device according to theinvention, the inner shaft is provided with three axial grooves, theaxial grooves being transversely located at 120° from one another. Ineach axial groove, an elastic member and two rolling tracks having theshape of an axial bar are mounted.

The balls are arranged in three axial rows, the axial rows beingtransversely located at 120° from one another.

The whole ball sleeve with the rolling tracks and the elastic axialflanges is closed at each axial end by a shoulder and a retaining ring.The retaining ring engages into each of the axial grooves of the innershaft.

The outer shaft is provided with three axial grooves transverselylocated at 120° from one another, which slide on the rows of balls. Theaxial grooves have the desired length for enabling the required axialsliding of the outer shaft and the inner shaft.

The coupling device according to the invention is very well appliedeither to the intermediate portion of an automotive vehicle steeringcolumn, or to the upper portion of an automotive vehicle steeringcolumn.

The coupling device of two shafts along the common axis thereofaccording to the invention has therefore the advantage of always havingtwo bearing areas for each of the two inner and outer shafts and foreach row of balls, which are always in contact, even if there is notorque transmission.

Further, there is a reduced axial stress which is necessary upon theline assembly. The accurate adjustment of the coupling device of theinvention enables the axial jerks upon driving the vehicle to beavoided, and ensures a good endurance by avoiding the onset of acoupling clearance. Moreover, upon passing of the torque, the axialstress is largely reduced due to the rolling and sliding contact.Finally, the coupling device can be mounted easily in the existingovercrowding of automotive vehicles steering columns.

Other characteristics and advantages of the present invention willappear clearly with the following description of several preferredembodiments of the invention, provided as non-limiting examples,referring to the corresponding appended drawings wherein:

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic perspective view of an automotive vehicle steeringsystem, wherein the coupling device of the invention is applied to theintermediate column portion;

FIG. 2 is an axial view of the intermediate portion of the automotivevehicle steering system of FIG. 1, wherein an embodiment of theinvention is depicted in a partial axial section view;

FIG. 3 is an exploded perspective view of the whole coupling device ofFIG. 2;

FIG. 4 is a cross-section along IV-IV of FIG. 2;

FIG. 5 is a cross-section along the plan of FIG. 4 of another embodimentof the invention;

FIG. 6 is a cross-section along the plan of FIG. 4 of another embodimentof the invention;

FIG. 7 is an enlarged partial view of FIG. 4 with a rolling track;

FIG. 8 is a view similar to FIG. 7 of another embodiment of the rollingtrack;

FIG. 9 is an enlarged partial view of the mounting of a row of balls ofFIG. 4;

FIG. 10 is a view similar to FIG. 9 with another rolling track accordingto the invention;

FIG. 11 is a view similar to FIG. 9 with another rolling track accordingto the invention;

FIG. 12 is a view similar to FIG. 9 with another rolling track accordingto the invention;

FIG. 13 is a view similar to FIGS. 9 to 12 with an elastic member in afree position;

FIG. 14 is a view similar to FIG. 13 with an elastic member incompressed position;

FIG. 15 is a perspective view of the inner shaft and the springcorresponding to FIG. 14;

FIG. 16 is an enlarged partial view of the mounting of a row of ballsalong the plan of FIG. 4, of another embodiment of the invention; and

FIG. 17 is a view similar to FIG. 16 of another embodiment of theinvention.

DETAILED DESCRIPTION

The invention relates to a rotatably coupling device of two shafts whichslide into each other along the common axis thereof.

This coupling device can be particularly well applied to an automotivevehicle steering system, as the one schematically depicted in FIG. 1.

The depicted steering system comprises a steering column with an uppercolumn portion 6 also known as column top, and an intermediate columnportion 7 also known as intermediate axis.

The upper column portion 6 is connected through the upper end thereof tothe steering wheel 5, and through the lower end thereof to theintermediate column portion 7.

The intermediate column portion 7 is connected through the upper endthereof to the upper column portion 6, and through the lower end thereofto the steering gear case 8 of the steering rod 9.

The intermediate column portion 7 is connected et each of the endsthereof through a Cardan joint referenced as 10 for the upper columnportion 6, and also referenced as 10 for the steering gear case 8.

In the following part, the description relates to a coupling devicewhich is arranged in the intermediate column portion 7. The couplingdevice of the invention can also be arranged in the upper column portion6.

An inner shaft 1 and an outer shaft 2 slide into each other along thedirection of the common axis 4 thereof, which is depicted in FIGS. 2 and3. The coupling device of both shafts comprises balls 3 in differentembodiments described below. The balls 3 are arranged between the innershaft 1 and the outer shaft 2. In the coupling device of the invention,each of said balls 3 is arranged, on the one hand, in a concave portionof the inner shaft 1, and, on the other hand, in a concave portion ofthe outer shaft 2.

Each of said balls 3 moves along two rolling tracks, which cooperatewith the concave portion of one of the two shafts and which pivot arounda joint axis. Each rolling track and the corresponding joint axis areparallel to the common axis 4. Each of the two rolling tracks is pushedby an elastic member, which is arranged and bears in said concaveportion. Each of said balls 3 moves directly against the concave portionof the other shaft.

The coupling device according to the invention is arranged such that atrest, when there is no torque transmission, and in operation, when thereis a torque transmission, the balls 3 are always in contact. On eitherside of a median plan going through the centre of the balls 3 and thecommon axis 4, each of the balls 3 is always in contact through abearing area with the corresponding rolling track arranged in one of thetwo shafts, and through a bearing area with the concave portion of theother shaft.

The whole intermediate column portion 7 in an axial view is depicted inFIG. 2. The inner shaft 1 and the outer shaft 2 slide with the balls 3along the common axis 4 thereof. The intermediate column portion 7 isconnected to the steering gear case 8 through the Cardan joint 10, andit is connected to the upper column portion 6 through the Cardan joint10.

The coupling device, represented in an exploded view in FIG. 3 and incross-section in FIG. 4, comprises balls 3 which are arranged in threeaxial rows 20. The axial rows 20 are transversely located at 120° fromone another. The inner shaft 1 is provided with three axial grooves 131,which are transversely located at 120° from one another. The outer shaft2 is provided with three axial grooves 132, which are transverselylocated at 120° from one another.

For each row 20 of balls 3, there is provided in the outer shaft 2aconcave portion having the shape of an axial groove 132, the section ofwhich comprises two concave sides 133, 134 being tilted with respect toeach other, which come into contact with the balls 3.

For each row 20 of balls 3, there is provided in the inner shaft 1aconcave portion having the shape of an axial groove 131, the section ofwhich comprises a bottom 135 and two flanks 136, 137. The bottom 135 issubstantially perpendicular to the median plan 30 going through thecommon axis 4 and the axis of the centres of the balls 3 in said row 20.

For each row 20 of balls 3, there are two rolling tracks 140 which arearranged on either side of the median plan 30. The rolling tracks 140cooperate with the concave portion having the shape of an axial groove131 of the inner shaft 1.

Each rolling track 140 has the shape of an axial bar, the section ofwhich has a bearing portion 141 and a pivot portion 142.

The bearing portion 141 has a bearing side 143, which is determined tocome into contact with the balls 3. The pivot portion 142 having arounded shape has a convex pivot side 144, which cooperates with aconcave rounded support side 138 or 139 of the axial groove 131. Theconcave rounded support side 138 joins the bottom 135 and the flank 136for one of the rolling tracks 140, and the concave rounded side 139joins the bottom 135 and the flank 137 for the other rolling track 140.

According to an essential characteristic of the invention shown indetail in FIGS. 7 and 8, the radius of the concave rounded support side138 and the radius of the concave rounded support side 139 are smallerthan the radius of the convex pivot side 144 of the correspondingrolling track 140. This characteristic enables to have two contact areasbetween the shaft 1 and the corresponding rolling track 140, the actionof which determines the position of an axis which is the joint axis 145of the pivot being parallel to the common axis 4.

Each of the two rolling tracks 140 is pushed by an elastic member 210which bears on the bottom 135 of the axial groove 131.

The coupling device shown in a cross-section according to FIG. 5comprises balls 3 which are arranged in three axial rows 20.

The axial rows 20 are transversely located at 120° from one another. Theinner shaft 1 is provided with three axial grooves 151, which aretransversely located at 120° from one another. The outer shaft 2 isprovided with three axial grooves 152, which are transversely located at120° from one another.

For each row 20 of balls 3, there is provided in the inner shaft 1aconcave portion having the shape of an axial groove 151, the section ofwhich comprises two concave sides 153, 154 being tilted with respect toeach other, which come into contact with the balls 3.

For each row 20 of balls 3, there is provided in the outer shaft 2aconcave portion having the shape of an axial groove 152, the section ofwhich comprises a bottom 155 and two flanks 156, 157. The bottom 155 issubstantially perpendicular to the median plan 30 going through thecommon axis 4 and the axis of the centres of the balls 3 in said row 20.

For each row 20 of balls 3, two rolling tracks 160 are arranged oneither side of the median plan 30. The rolling tracks 160 cooperate withthe concave portion having the shape of an axial groove 152 of the outershaft 2. Each rolling track 160 has the shape of an axial bar, thesection of which has a bearing portion 161 and a pivot portion 162.

The bearing portion 161 has a bearing side 163, which is determined tocome into contact with the balls 3. The pivot portion 162 having arounded shape has a convex pivot side 164, which cooperates with aconcave rounded support side 158 or 159 of the axial groove 151. Theconcave rounded support side 158 joins the bottom 155 and the flank 156for one of the rolling tracks 160, and the concave rounded side 159joins the bottom 155 and the flank 157 for the other rolling track 160.

According to an essential characteristic of the invention shown indetail in FIGS. 7 and 8, the radius of the concave rounded support side158 and the radius of the concave rounded support side 159 is smallerthan the radius of the convex pivot side 164 of the correspondingrolling track 160. This characteristic enables to have two contact areasbetween the shaft 2 and the corresponding rolling track 160, the actionof which determines the position of an axis which is the joint axis 165of the pivot being parallel to the common axis 4.

Each of the two rolling tracks 160 is pushed by an elastic member 210which bears on the bottom 155 of the axial groove 152.

The coupling device shown in cross-section in FIG. 16 comprises balls 3which are arranged in three axial rows 20.

The axial rows 20 are transversely located at 120° from one another. Theinner shaft 1 is provided with three axial grooves 171, which aretransversely located at 120° from one another. The outer shaft 2 isprovided with three axial grooves 172, which are transversely located at120° from one another.

For each row 20 of balls 3, there is provided in the outer shaft 2aconcave portion having the shape of an axial groove 172, the section ofwhich comprises two concave sides 173, 174 being tilted with respect toeach other, which come into contact with the balls 3.

For each row 20 of balls 3, there is provided in the inner shaft 1aconcave portion having the shape of an axial groove 171, the section ofwhich comprises a bottom 175 and two flanks 176, 177. The bottom 175 issubstantially perpendicular to the median plan 30 going through thecommon axis 4 and the axis of the centres of the balls 3 in said row 20.

For each row 20 of balls 3, two rolling tracks 180 are arranged oneither side of the median plan 30. The rolling tracks 180 cooperate withthe concave portion having the shape of an axial groove 171 of the innershaft 1. Each rolling track 180 has the shape of an axial bar, thesection of which has a bearing portion 181 and a pivot portion 182.

The bearing portion 181 has a bearing side 183, which is determined tocome into contact with the balls 3. The pivot portion 182 having arounded shape has a concave pivot side 184, which cooperates with aconvex rounded support side 178 or 179 of the axial groove 171. Theconvex rounded support side 178 joins the bottom 175 and the flank 176for one of the rolling tracks 180, and the convex rounded side 179 joinsthe bottom 175 and the flank 177 for the other rolling track 180.

According to an essential characteristic of the invention, the radius ofthe convex rounded support side 178 and the radius of the convex roundedsupport side 179 is larger than the radius of the concave pivot side 184of the corresponding rolling track 180. This characteristic enables tohave two contact areas between the shaft 1 and the corresponding rollingtrack 180, the action of which determines the position of an axis whichis the joint axis 185 of the pivot being parallel to the common axis 4.

Each of the two rolling tracks 180 is pushed by an elastic member 210which bears on the bottom 175 of the axial groove 171.

The coupling device shown in cross-section in FIG. 17 comprises balls 3which are arranged in several axial rows 20.

The axial rows 20 are transversely located at 120° from one another. Theinner shaft 1 is provided with three axial grooves 191, which aretransversely located at 120° from one another. The outer shaft 2 isprovided with three axial grooves 192, which are transversely located at120° from one another.

For each row 20 of balls 3, there is provided in the inner shaft 1aconcave portion having the shape of an axial groove 191, the section ofwhich comprises two concave sides 193, 194 being tilted with respect toeach other, which come into contact with the balls 3.

For each row 20 of balls 3, there is provided in the outer shaft 2aconcave portion having the shape of an axial groove 192, the section ofwhich comprises a bottom 195 and two flanks 196, 197. The bottom 195 issubstantially perpendicular to the median plan 30 going through thecommon axis 4 and the axis of the centres of the balls 3 in said row 20.

For each row 20 of balls 3, two rolling tracks 200 are arranged oneither side of the median plan 30. The rolling tracks 200 cooperate withthe concave portion having the shape of an axial groove 192 of the outershaft 2. Each rolling track 200 has the shape of an axial bar, thesection of which has a bearing portion 201 and a pivot portion 202.

The bearing portion 201 has a bearing side 203, which is determined tocome into contact with the balls 3. The pivot portion 202 having arounded shape has a concave pivot side 204, which cooperates with aconvex rounded support side 198 or 199 of the axial groove 191. Theconvex rounded support side 198 joins the bottom 195 and the flank 196for one of the rolling tracks 200, and the convex rounded side 199 joinsthe bottom 195 and the flank 197 for the other rolling track 200.

According to an essential characteristic of the invention, the radius ofthe convex rounded support side 198 and the radius of the convex roundedsupport side 199 is larger than the radius of the concave pivot side 204of the corresponding rolling track 200. This characteristic enables tohave two contact areas between the shaft 2 and the corresponding rollingtrack 200, the action of which determines the position of an axis whichis the joint axis 205 of the pivot being parallel to the common axis 4.

Each of the two rolling tracks 200 is pushed by an elastic member 210which bears on the bottom 195 of the axial groove 192.

Whatever the embodiment depicted in FIGS. 2 to 17, each of the tworolling tracks 140, 160, 180, 200 is pushed by an elastic member whichis a metal spring 210. The spring 210 is made of an axial body 211 whichis provided with elastic members 216. The body 211 comprises on eithertransverse side an axial edge 212 and 213, as shown in details in FIGS.13, 14 and 15. The body 211 further comprises at each axial end a staple214 and 215. The elastic members are transverse tabs 216, which arearranged directly by cutting the body 211. The transverse tabs 216 areheld alternately on an axial edge 212, and then on the other axial edge213. The body 211 is mounted in the bottom 135, 155, 175, 195 of thecorresponding concave portion of the relevant shaft, having a shapebeing conjugated with that of said bottom, that is bulged, in otherwords convex. Said bottom comprises, at each transverse end, a concaveshape receiving the corresponding axial edge 212, 213 of said spring210, of which both staples 214, 215 hold on the corresponding shaft.

In the embodiments shown in the FIGS., the radius of the support side ofthe shaft 1 or 2 and the radius of the pivot side of the relevantrolling track have constant values. In other embodiments shown in FIG.8, the radius of the pivot side is progressive. In other not shownembodiments of the invention, it is the radius of the support side ofthe shaft 1 or 2 which is progressive. Finally, in other not shownembodiments of the invention, it is the radius of the pivot side and theradius of the support side which are progressive. As particularly shownin FIGS. 6, 7, 8 and 9, each of the two rolling tracks 140, 160, 180,200 has the bearing portion 141, 161, 181, 201 provided with a bearingside 143, 163, 183, 203 of the balls 3 which is flat. As shown in FIG.10, the bearing side of the balls is convex, while according to FIG. 11,the bearing side is concave, and according to FIG. 12, the bearing sideof the balls has a double concavity.

As shown in FIGS. 3 to 5, the balls 3 can be arranged in three axialrows 20, the axial rows 20 being transversely located at 120° from oneanother. The inner shaft 1 is provided with three axial grooves 131,151, 171, 191, the axial grooves 131, 151, 171, 191 being transverselylocated at 120° from one another. The outer shaft 2 is provided withthree axial grooves 132, 152, 172, 192, the axial grooves 132, 152, 172,192 being transversely located at 120° from one another.

As is the case for FIG. 6, the balls 3 can be arranged in twodiametrically opposed axial rows 20. The inner shaft 1 is provided withtwo diametrically opposed axial grooves 131, 151, 171, 191; and theouter shaft 2 is provided with two diametrically opposed axial grooves132, 152, 172, 192.

As particularly shown in FIG. 9, male grooves 23 and female grooves 24having conjugated profiles with some clearance, are provided on thesliding side 21 of the inner shaft 1 and on the sliding side 22 of theouter shaft 2; the male grooves having an apex 25 and two flanks 27, thefemale grooves 24 having a bottom 26 and two flanks 28. Thus, in casethe balls 3 are lost, the torque can still be transmitted between theinner shaft 1 and the outer shaft As it is particularly the case ofFIGS. 4, 6, and 16, the elastic members or springs 210 can be arrangedin the inner shaft 1 and push both rolling tracks 140, 180 whichcooperate with the inner shaft.

As particularly for FIGS. 5 and 17, the elastic members or springs 210can be arranged in the outer shaft 2 and push both rolling tracks 160,200 which cooperate with the outer shaft.

While remaining under the scope of the invention, some of the elasticmembers or springs 210 can also be arranged in the inner shaft 1, andthe others in the outer shaft 2, said elastic members pushing bothcorresponding rolling tracks, which cooperate with the relevant shaft.

In the embodiment of FIGS. 3, 4 and 16, the inner shaft 1 is providedwith three axial grooves 131, 171. The axial grooves 131, 171 aretransversely located at 120° from one another. In each axial groove 131,171, an axial elastic member or spring 210 and two rolling tracks 140,180 having the shape of an axial bar are mounted.

The balls 3 are arranged in three axial rows 20, which are transverselylocated at 120° from one another.

The whole assembly of balls 3 with the rolling tracks 140, 180 and theelastic members or springs 210 is closed at each axial end by a shoulder15 and by a retaining ring 12. The retaining ring 12 engages into eachof the axial grooves 131, 171 of the inner shaft 1.

The outer shaft 2 is provided with three axial grooves 132, 172transversely located at 120° from one another, which slide on the rows20 of balls 3. The axial grooves 132. 172 should have the desired lengthin order to enable the required axial sliding of the outer shaft 2 andthe inner shaft 1.

The essential characteristics of the invention are reminded thereafter.

The balls are in contact, on the one hand, with one of the shafts and,on the other hand, with both rolling tracks. The rolling tracks are incontact with the other shaft and can pivot in the shaft. The rollingtracks are in contact with elastic members which are intended tomaintain the contact between the rolling tracks and the balls at onepoint.

Upon assembling the system, the elastic members enable the sizevariations of the different components to be compensated. It can becalled tolerance absorption through elastic member deformation.

Upon applying a torque, the load is transmitted from the tube on theshaft through the balls and the rolling tracks. The load applicationline goes through the centre of the ball and the pivot of the rollingtrack. Thus, the load is directly taken by the shaft without biasing theelastic member. The angular rigidity is very important and independentof the stiffness of the elastic members.

Upon an axial movement of the tube with respect to the shaft, thesliding stress of the system is a function of the stresses on the ballsinserted by the elastic members.

Upon applying a torque, the sliding stress of the system is then afunction of stresses on the balls inserted by the elastic members andthe torque applied to the system.

1. A coupling device for an inner shaft and an outer shaft slidingwithin each other along the direction of the common axis thereof, withballs provided between the two shafts, each of said balls beingprovided, on the one hand, in a concave portion of the inner shaft, and,on the other hand, in a concave portion of the outer shaft, each of saidballs moving along two rolling tracks which cooperate with the concaveportion of one of the two shafts, each ball moving directly against theconcave portion of the other shaft; said rolling tracks pivoting in thecorresponding concave portion, and being pushed by an elastic memberthat bears in said concave portion, wherein: the two rolling tracks areprovided on either side of a median plan going through the common axisand the centre of said balls; each of the two rolling tracks has: abearing portion, with a bearing side of each of said balls; and a pivotportion, with a rounded pivot side applying against a rounded supportside of the corresponding concave portion of the shaft; the radius ofthe support side of the shaft is different from the radius of the pivotside of the rolling track in order to have two contact areas whichdetermine the position of a joint axis of the pivot being parallel tothe common axis so that: at rest, when there is no torque transmission,and in operation when there is a torque transmission, each of said ballsis still contacting on either side of the median plan, through a bearingarea a corresponding rolling track provided in one of the two shafts,and through a bearing area the concave portion of the other shaft. 2.The coupling device according to claim 1, wherein: the radius of theconcave support side of the shaft is smaller than the radius of theconvex pivot side of the rolling track.
 3. The coupling device accordingto claim 1, wherein: the radius of the convex support side of the shaftis larger than the radius of the concave pivot side of the rollingtrack.
 4. The coupling device according to claim 1, wherein, for each ofthe two rolling tracks, the radius of the support side of the shaft theradius of the pivot side of the rolling track are constant.
 5. Thecoupling device according to claim 1, wherein, for each of the tworolling tracks, the radius of the pivot side is progressive.
 6. Thecoupling device according to claim 1, wherein for each of the tworolling tracks, the radius of the support side and the radius of thepivot side are progressive.
 7. The coupling device according to claim 1,wherein, for each of the two rolling tracks, the bearing portion has abearing side of the balls which is plane.
 8. The coupling deviceaccording to claim 1, wherein, for each of the two rolling tracks, thebearing portion has a bearing side of the balls which is convex.
 9. Thecoupling device according to claim 1, wherein, for each of the tworolling tracks, the bearing portion has a bearing side of the ballswhich is concave.
 10. The coupling device according to claim 1, wherein,for each of the two rolling tracks, the bearing portion has a bearingside of the balls which has a double concavity.
 11. The coupling deviceaccording to claim 1, wherein the elastic member is a spring, made of abody provided with elastic members and comprising an axial edge oneither side and a staple at each axial end; said body being mounted in abottom of the corresponding concave portion of the shaft and having ashape conjugated with said bottom, i.e. bulged or convex, said bottomhaving at each transverse end a concave shape receiving thecorresponding axial edge of said spring of which both staples hold onthe corresponding shaft.
 12. The coupling device according to claim 11,wherein the elastic members are transverse tabs directly arranged bycutting the body, said tabs holding alternatively on an axial edge andthen on the other edge.
 13. The coupling device according to claim 1,wherein male grooves and female grooves with conjugated profiles havingsome clearance, are provided on the inner shaft and the outer shaft suchthat, in case the balls are broken, the torque can still be transmittedbetween the inner shaft and the outer shaft.
 14. The coupling deviceaccording to claim 1, wherein each of the elastic members is arranged inthe inner shaft and pushes both corresponding rolling tracks whichcooperate with the inner shaft.
 15. The coupling device according toclaim, wherein each elastic member is arranged in the outer shaft andpushes both corresponding rolling tracks which cooperate with the outershaft.
 16. The coupling device according to claim 1, wherein eachelastic member is provided for some of them in the inner shaft and forthe others in the outer shaft, each of said elastic members pushing bothcorresponding rolling tracks, which cooperate with the considered shaft.17. The coupling device according to claim 2, wherein the balls arearranged in two axial rows; for each row of balls, there is provided inthe outer shaft a concave portion having the shape of an axial groove,the section of which comprises two concave sides being tilted withrespect to each other, which come into contact with the balls, for eachrow of balls, there is provided in the inner shaft a concave portionhaving the shape of an axial groove, the section of which has a bottomand two flanks, the bottom being substantially perpendicular to themedian plan going through the common axis and the axis of the centres ofthe balls in said row, for each row of balls, two rolling tracks arearranged on either side of the median plan and cooperate with theconcave portion having the shape of an axial groove of the inner shaft,each rolling track has the shape of an axial bar of which the sectionhas: a bearing portion with a bearing side determined to come intocontact with the balls; a pivot portion having a rounded shape with aconvex pivot side, which cooperates with a concave rounded support sidejoining the bottom and the corresponding flank of the axial groove, inorder to have two contact areas determining the position of the jointaxis of the pivot being parallel to the common axis; each of the tworolling tracks is pushed by a spring which bears on the bottom of theaxial groove.
 18. The coupling device according to claim 2, wherein theballs are arranged in several axial rows; for each row of balls, thereis provided in the inner shaft a concave portion having the shape of anaxial groove, the section of which comprises two concave sides tiltedwith respect to each other, which come into contact with the balls; foreach row of balls, there is provided in the outer shaft a concaveportion having the shape of an axial groove, the section of whichcomprises a bottom and two flanks, the bottom being substantiallyperpendicular to the median plan going through the common axis and theaxis of the centres of the balls in said row; for each row of balls, tworolling tracks are arranged on either side of the median plan andcooperate with the concave portion having the shape of an axial grooveof the outer shaft, each rolling track has the shape of an axial bar,the section of which has: a bearing portion with a bearing sidedetermined to come into contact with the balls; a pivot portion having arounded shape with a convex pivot side, which cooperates with a concaverounded support side, joining the bottom and the corresponding flank ofthe axial groove, in order to have two contact areas determining theposition of the joint axis of the pivot being parallel to the commonaxis; each of the two rolling tracks is pushed by a spring which bearson the bottom of the axial groove.
 19. The coupling device according toclaim 3, wherein the balls are arranged in several axial rows; for eachrow of balls, there is provided in the outer shaft a concave portion inthe shape of an axial groove, the section of which comprises two concavesides being tilted with respect to each other, which come into contactwith the balls; for each row of balls, there is provided in the innershaft a concave portion having the shape of an axial groove, the sectionof which comprises a bottom and two flanks, the bottom beingsubstantially perpendicular to the median plan going through the commonaxis and the axis of the centres of the balls in said row; for each rowof balls, two rolling tracks are arranged on either side of the medianplan and cooperate with the concave portion having the shape of an axialgroove of the inner shaft, each rolling track has the shape of an axialbar, the section of which has: a bearing portion with a bearing sidedetermined to come into contact with the balls; a pivot portion having arounded shape with a concave pivot side, which cooperates with a convexrounded support side, joining the bottom and the corresponding flank ofthe axial groove, in order to have two contact areas determining theposition of the joint axis of the pivot being parallel to the commonaxis; and each of the two rolling tracks is pushed by a spring whichbears on the bottom of the axial groove.
 20. The coupling deviceaccording to claim 3, wherein the balls are arranged in several axialrows; for each row of balls, there is provided in the inner shaft aconcave portion having the shape of an axial groove, the section ofwhich comprises two concave sides being tilted with respect to eachother, which come into contact with the balls; for each row of balls,there is provided in the outer shaft a concave portion having the shapeof an axial groove, the section of which comprises a bottom, and twoflanks, the bottom being substantially perpendicular to the median plangoing through the common axis and the axis of the centres of the ballsin said row; for each row of balls, two rolling tracks are arranged oneither side of the median plan and cooperate with the concave portionhaving the shape of an axial groove of the outer shaft, each rollingtrack has the shape of an axial bar, the section of which has: a bearingportion with a bearing side determined to come into contact with theballs; a pivot portion having a rounded shape with a concave pivot side,which cooperates with a convex rounded support side, joining the bottomand the corresponding flank of the axial groove, in order to have twocontact areas determining the position of the joint axis of the pivotbeing parallel to the common axis; and each of the two rolling tracks ispushed by a spring which bears on the bottom of the axial groove. 21.The coupling device according to claim 17, wherein the balls arearranged in three axial rows, the axial rows being transversely locatedat 120° from one another; the inner shaft is provided with three axialgrooves, the axial grooves being transversely located at 120° from oneanother; and the outer shaft is provided with three axial grooves, theaxial grooves being transversely located at 120° from one another. 22.The coupling device according to claim 17, wherein: the balls arearranged in two diametrically opposed axial rows; the inner shaft isprovided with two diametrically opposed axial grooves; the outer shaftis provided with two diametrically opposed axial grooves.
 23. Thecoupling device according to claim 1, wherein: the inner shaft isprovided with three axial grooves, the axial grooves being transverselylocated at 120° from one another, in each axial groove, an axial metalspring and two rolling tracks having the shape of an axial bar aremounted; the balls are arranged in three axial rows, the axial rowsbeing transversely located at 120° from one another; the assembly ofballs with the rolling tracks and the metal springs is closed at eachend by a shoulder and a retaining ring which engages in each of theaxial grooves of the inner shaft; and the outer shaft is provided withthree axial grooves transversely located at 120° from one another, whichslide on the rows of balls, the axial grooves having the desired lengthfor the required axial sliding of the outer shaft and the inner shaft.24. The coupling device according to claim 1, wherein it applies to theintermediate portion of an automotive vehicle steering column.
 25. Thecoupling device according to claim 1, wherein it applies to the upperportion of an automotive vehicle steering column.